1. Field of the Invention
This invention relates to a method for processing a signal and an apparatus for processing a signal, and more particularly this invention is preferably applied to a signal processing method and a signal processing apparatus in which a video signal taken by a photographing device provided with an optical system such as a video-camera or a still-camera or the like is processed.
2. Description of the Related Art
It has become well known to provide, as a photographing device, a so-called digital video camera (photographing a motion picture) or a digital still-camera (photographing a still picture) or the like, for example.
In such a photographing device as described above, its operation is carried out such that an image photographed through an optical system is taken into the device, although it has been known that a degree of resolution of the photographed image is deteriorated more than that of a subject due to an aberration of a lens installed in the optical system.
In view of this fact, it has already been provided to correct a degree of resolution of the image through an aperture control for an image signal of the photographed image. The aperture control used herein is defined as a signal processing in which a correction is carried out for improving a degree of apparent resolution while a high regional component of a brightness signal of a photographed image signal, for example, is intensified with the result that an edge part of the photographed image (in this case, this is defined as an interface part of a brightness in the image) is made apparent.
It has already been known in the art that a degree of deterioration in resolution of the photographed image is also changed in response to a condition of the image during a photographing operation and the resolution of the image is made remarkably different by changing a degree of opening of the aperture, for example.
However, in the case of the usual aperture control performed up to now, it has been carried out that a predetermined gain which has been uniformly set is applied to an image signal of the photographed image so as to amplify an amplitude of the high level component. Due to this fact, devices have not been provided which perform a correction in compliance with a variation of a resolution caused by a variation of a degree of opening of the iris diaphragm as described above or a variation in state of a zoom position of a zoom lens.
Due to this fact, there was a problem that xe2x80x9cirregular patternsxe2x80x9d were generated in the resolution of the photographed image to cause a normal image not to be attained at a glance because of a variation in state of an iris diaphragm or a zoom position during photographing operation irrespective of the fact that a photographing was carried out by the same photographing device.
In view of the foregoing, the present invention performs a correction for variation of a resolution of image signal generated in response to a variation in state of an optical system in the photographing device to cause its value to become approximately constant by an image signal processing method for processing an image signal for a photographed image in order to solve the aforesaid problems.
In addition, the image signal processing device for processing an image signal for photographed image is provided with a resolution correcting means for correcting a variation of resolution of the aforesaid image signal generated in response to a variation in state of an optical system of the photographing device in such a way that its value may become substantially constant.